I don't think that was a dream. The usual trope is they totally did it and she put her cloths back on after she fainted from the excitement and alcohol. Which causes tomoko to assume it was a dream.
Agreed, it lacks the usual manga conventions of using a black outline/fadeout onto the imaginary scene.
/a/ pointed out that these two are pretty much Katou and Tomoko from Watamote with the serial number filed off and now I'm laughing my ass off harder at Nikaidou's antics.
I mean, is ultimately harmless and can be easily ignored if you aren't comfortable/into that, but the sudden change to outright ban things they were previously ok with, sets a worrying precedent for future games.